This invention relates to hydraulic filters and more particularly to a dual filter arrangement which alternately and selectively establishes fluid communication and isolation for on-duty and off-duty filter elements and interlocks against inadvertent switchovers.
Conventional filter arrangements of this type are often large and unwieldy, of relatively high cost and require valving arrangements which have critical dimensions and which are difficult to manufacture. Typical of these are the ball valve type filter units which require precision machining and finishing of spherical surfaces and precise alignment techniques.
One example of prior art device is shown in U.S. Pat. No. 3,618,781. In this form of apparatus which describes dual filter housings and a central valve housing, upper and lower valve members are rotated by a common handle so that valving surfaces cooperate with valve seats formed in the bore of the valve housing in a metal to metal sliding valve arrangement.
Another example of prior art apparatus of this type is shown in U.S. Pat. No. 3,915,866. In this high pressure dual filter assembly, a central selector valve rotatably selects one of dual filter devices by means of a close, sliding, lapped fit between the ported valve member and the valve housing bore. In this arrangement, a balancing valve is utilized to supply fluid pressure to opposite sides of the selector valve to facilitate rotation of the latter.